Afatinib is a tyrosine kinase inhibitor disclosed in U.S. Pat. Nos. RE43,431 and 6,251,912. Afatinib is depicted by Formula Ia:

Afatinib is presented as the dimaleate salt and is chemically designated as 2-butenamide, N-[4-[(3-chloro-4-fluorophenyl)amino]-7-[[(3S)-tetrahydro-3-furanyl]oxy]-6-quinazolinyl]-4-(dimethylamino)-,(2E)-,(2Z)-2-butenedioate (1:2) having the structure depicted by Formula I:

Processes for the preparation of 4-dimethylaminocrotonic acid or its salts are disclosed in U.S. Pat. No. 7,126,025 and U.S. Publication No. 2012/0046494.
U.S. Pat. No. 7,126,025 discloses a process for the preparation of 4-dimethylaminocrotonic acid or its salts by reacting but-2-enoic acid with chlorotrimethylsilane in pyridine to obtain trimethylsilylcrotonate, which is brominated with a brominating agent under free radical conditions and in the presence of methylene chloride, acetonitrile, 1,2-dichloroethane, carbon tetrachloride, or ethyl acetate to give trimethylsilyl-4-bromocrotonate. The bromocrotonate compound is treated with dimethylamine in tetrahydrofuran to provide the 4-dimethylaminocrotonic acid.
U.S. Pat. No. 7,126,025 also discloses a process for the preparation of 4-dimethylaminocrotonic acid by treating methyl or ethyl 4-bromocrotonate with dimethylamine to provide methyl or ethyl 4-dimethylaminocrotonate, which is hydrolyzed to provide the 4-dimethylaminocrotonic acid.
U.S. Publication No. 2012/0046494 discloses a process for the preparation of 4-dimethylaminocrotonic acid or its salts by converting alkyl 4-chloro-3-hydroxy butyrate to alkyl 4-hydroxy crotonate, which is brominated to obtain alkyl 4-bromo crotonate. The alkyl 4-bromo crotonate is treated with dimethyl amine to provide alkyl 4-dimethylaminocrotonate, which is hydrolyzed to get the 4-dimethylaminocrotonic acid.
The use of pyridine or carbon tetrachloride is toxic to humans and therefore their use for the manufacture of a drug substance is not advisable. The bromocrotonate compounds, being lachrymatory in nature, are difficult to handle on an industrial scale.
The present invention provides a faster, more efficient, and industrially feasible process for the preparation of 4-dimethylaminocrotonic acid of Formula II, which is used as an intermediate for the preparation of afatinib or its salts.